1. Field of the Invention
The present invention relates to a cooling system for cooling a substance to be cooled by producing cold with a cold-accumulating refrigerator.
2. Description of Related Art
Japanese Examined Patent Publication (KOKOKU) No. 45-27,634 discloses a conventional cooling system which employs a cold-accumulating refrigerator, and which is constructed as illustrated in FIG. 21. As illustrated in FIG. 21, this conventional cooling system comprises a cold gas refrigerator 101 which operates as a cold source under reverse Stirling cycle, and a cooling circuit 120 which operates as a refrigerant circuit for delivering cold to a substance 110 to be cooled.
The cold gas refrigerator (hereinafter simply referred to as "refrigerator") 101 includes a cylinder 100, a piston 102 which reciprocates in the cylinder 100, a displacer 103 which reciprocates with a predetermined phase difference with respect to the piston 102, a chiller 106 which communicates with a compression chamber 104 disposed between the piston 102 and the displacer 103, a freezer 108 which is disposed in an expansion chamber 105 placed between the displacer 103 and a top end of the cylinder 101, and a cold accumulator 107 which is disposed between the chiller 106 and the expansion chamber 105.
The cooling circuit 120 includes a compressor 121, a piping 124, and a counterflow heat exchanger 123 which is disposed between the piping 12 and the compressor 121. The piping 124 includes a plurality of heat exchangers 125 for conducting cold, and a plurality of heat exchangers 126 for cooling a substance 110 to be cooled. The heat exchangers 125 are thermally brought into contact with the freezer 108. The heat exchangers 125 and the heat exchangers 126 are disposed alternately in series.
In the thus constructed conventional cooling system, the piston 102 compresses a working medium to produce heat in the compression chamber 104 of the refrigerator 101 (i.e., isothermal compression). Then, the displacer 103 moves toward the piston 102 to cool and pass the working medium through the cold accumulator 107 (i.e., constant-volume cooling). Further, the piston 102 retracts to produce cold in the expansion chamber 105 (i.e., isothermal expansion), and the cold is absorbed by the other working medium which flows in the cold-conducting heat exchanger 125 being thermally brought into contact with the freezer 108. Furthermore, the displacer 103 moves to its top dead center, and thereby the working medium cools the cold accumulator 107 and returns to the compression chamber 104 (i.e., constant-volume heating).
The other working medium flows in the cooling circuit 120. When it flows in the cold-conducting heat exchanger 125, its heat is absorbed, and cold thus produced is conducted to the heat exchanger 126 for cooling. Accordingly, the substance 110 to be cooled is cooled. The counterflow heat exchanger 123 cools the high-temperature working medium, which is delivered from the compressor 121, by means of the low-temperature working medium which returns to the compressor 121.
The thus constructed cooling system can employ a helium gas as the working media, and can be applied to home-use refrigerators, air conditioners, etc. When its refrigerator employs a multi-staged expansion arrangement, and when its cooling circuit utilizes a Joule-Thomson (hereinafter referred to as "J-T") circuit, it is possible to attain a liquefied helium temperature as low as 4.2 K., and to cool superconducting magnets.
According to the equation defining the Carnot efficiency, the lower the temperature of the cold source is, the worse the efficiency is for cooling a substance to be cooled. When the conventional cooling system is considered in terms of efficiency from this perspective, it takes out cold produced at the expansion chamber 105, and gives the cold to the freezer 108. The cold-conducting heat exchangers 125 receive the cold, and transfer it to the heat exchangers 126 for cooling. Then, the substance 110 to be cooled is cooled. Thus, the conventional cooling system does not utilize the cold produced by the entire refrigerator 101 effectively.
Specifically, the refrigeration Q taken out to the freezer 108 is used to cancel the refrigeration Q.sub.1 consumed to cool the substance 110 to be cooled, the refrigeration Q.sub.2 consumed at the counterflow heat exchanger 123, and the heat Q.sub.3 (i.e., conduction heat and radiation heat) intruding into the counterflow heat exchanger 123 from the surroundings; namely: the refrigeration Q equals Q.sub.1 +Q.sub.2 +Q.sub.3 (i.e., Q.sub.1 =Q.sub.1 +Q.sub.2 +Q.sub.3). Let us assume that the freezer 108 is a cold source of a predetermined temperature which corresponds to the cold head of refrigerator 101. The cold is produced from the predetermined temperature which shows a specific temperature difference with respect to the temperature of the substance 110 to be cooled, it is not produced from a high temperature which is higher than the predetermined temperature. In other words, in a temperature range of from the temperature of the refrigerator cold head to the temperature of the highly-pressurized working medium itself delivered from the compressor 121, the refrigerations Q.sub.2 and Q.sub.3 are consumed to cool the highly-pressurized working medium, being delivered from the compressor 121, by means of the counterflow heat exchanger 123. As a result, the cold is not produced from the high temperature which is higher than the predetermined temperature and which enables to efficiently carry out cooling.